HIV pathogenesis in infected individuals and cytopathic effects in tissue culture are tightly correlated with viral load and replication. We propose to study several unique HIV-1 clones with attenuated cytopathic effects (CPE) derived from long term non progressors with high viral load, which will allow us to separate the determinants of viral load and replication from the determinants of HIV-1 pathogenesis. Most HIV-1 isolates from long-term non-progressors (LTNP) are CCR5-tropic (R5) and replicate poorly in vivo and in tissue culture, in contrast, some LTNP paradoxically have moderate to high viral load (LTNP-HVL), equivalent to that seen in individuals who progress to AIDS. We hypothesize and have preliminary data which indicate, that some LTNP-HVL derived HIV-1 clones are equally replication competent but less cytopathic than HIV-1 clones from individuals who progress to AIDS. The studies proposed in this application will use these unique clones to define the genetic determinants and mechanisms of pathogenesis of all HIV-1 clones. These unique HIV-1 clones may allow us to separate determinants of viral pathogenesis from determinants of viral replication, which may impact the development of AIDS therapeutics and vaccines. We have the following specific aims: 1. Characterize the replication and cytopathic effects, of R5 HIV-1 isolates from LTNP-HVL in FTOC, tonsil histoculture and SCID-hu mice. We will further characterize two HIV-1 clones with attenuated CPE that we have started to study and will characterize at least two more of these unique and informative HIV-1 biological clones in FTOC and tonsil histoculture. The most attenuated HIV-1 clones will also be studied in SCID-hu mice. 2. Characterize the Env and Nef associated phenotypes of R5 HIV-1 isolates from LTNP-HVL in tissue culture. These phenotypes will be studied since they have been linked to pathogenesis of HIV-1 due to their variation between HIV-1 clones from progressors and non-progressors and from early to late stages of infection. [unreadable] [unreadable]